docs: def Cross(self, A=[(0, 0), (10, 10)], B=[(0, 10), (100, 0)]):
  
          '''
          Return the crosspoint of two line A and B.
          :param A: first line
          :type A: a list consist of two tuples, beginning and end point of the line
          :param B: second line
          :type B: a list consist of two tuples, beginning and end point of the line
          :return: the crosspoint of A and B
          :rtype: a list consist of two numbers, the x-y of the crosspoint
          '''
  
          x0, y0 = A[0]
          x1, y1 = A[1]
          x2, y2 = B[0]
          x3, y3 = B[1]
  
          b1 = (y1 - y0) / (x1 - x0)
          b2 = (y3 - y2) / (x3 - x2)
          c1 = y0 - b1 * x0
          c2 = y2 - b2 * x2
  
          x = (c2 - c1) / (b1 - b2)
          y = b1 * x + c1
  
          return ([x, y])